The average person is not trained to think logically. Worse, they are too often compromised by religious indoctrination, which starts frequently from long before they learned to think at all. Religion projects its self-perceived importance onto anyone it touches and as strongly as it can. There is something more than this life, it says; that something is revealed through faith; faith is a virtue - this crap has been circulating throughout humanity for more years than any of us care to count. While atheism as a concept has been around for almost as long as theism is, it is only recently that those above-mentioned concepts and others stemming from them have been sufficiently challenged to effectively cast doubt on them.

If atheism is to succeed, there is a lot that has to be countered, and in addition to all I listed above, add one more: the laziness of people and their unwillingness to work toward an answer which may not be immediately apparent or intuitively obvious.

I have to remind myself that emotional thinking always assumes domination over rational thinking unless you make a conscious effort and a definite habit of relying on logic. There may be an evolutionary reason for this in the need to act first and think later when danger threatens.

This dominance of emotion over reason accounts for the response conservative radio commentators and preachers are able to produce. It's the oldest trick in the book of persuasion: convince people there is danger lurking everywhere and you have their consent before they realize what they're thinking.

I think that there is not a clear line between emotional and rational thinking, but rather it's a continuum of experience / response modified by slowing down and rationalizing when we can afford to do so. You don't apply rational formulae on the tennis court or battlefield, but just go out there and do it, and maybe rationalize later when the pressure is off. Our brains react quickly to stimuli, and more slowly build a rationale about how and why we reacted, and how to modify future reactions. But it's the same body that did all that, and it's not neatly compartmentalized into "emotional" or "rational". We can use those tags to make rhetorical points, but it's important to realize that such distinctions are created for that purpose and not a natural division.

In a "snap-decision" situation, thinking utterly rationally may not be a facile skill to most people or even most atheists, but I suspect that as people incorporate rationality in their lives over time, they can become more at home with rational thought and associated decision-making. I wouldn't expect this process to be so refined that those involved would become de-facto Vulcans, but at least to be able to remove a fair measure of the irrational from their everyday lives.

As with so many other things, practice makes ... well, maybe not perfect, but Better.

I'm guessing that the "wouldn't matter" vote is on a steady trend upwards, on par with the steady growth of atheism and agnosticism. To me, that's a better answer than "more likely". I wouldn't want atheist to be my determining factor in voting for a candidate. Schmucks come in all varieties.